1. Field of the Invention
The present invention relates to a fuel flow controller for a gas-turbine combustor provided with a plurality of premix burners.
2. Description of the Related Art
Recent gas turbines trend to increase the ratio of premix combustion to diffusion combustion to reduce Nox emission of the gas-turbine combustor. Premix combustion, as compared with diffusion combustion, is effective in reducing the production of Nox and, on the other hand, narrows the range of stable combustion. It is important to develop a gas-turbine combustor capable of operating in the predetermined range of fuel-air ratio for premix combustion to ensure the stable operation of a gas turbine in the entire range of operating load.
Generally, a gas turbine operates in a diffusion combustion mode in a low-load period from the start of operation to a low-load operating state in which the gas turbine operates under a low load in the range of 5 to 35% of the rated load in which stable premix combustion can be sustained, and the ratio of premix combustion is increased gradually as the load on the gas turbine increases from the low load to the rated load. Therefore, the emission of Nox during low-load operation may be reduced by employing a premix combustion arrangement provided with a plurality of premix burners and capable of realizing conditions for stable combustion during low-load operation. Such a premix combustion arrangement requires the development of a gas controller for controlling the flow rates of the gas to be supplied to the plurality of premix burners.
An invention disclosed in JP-A No. 6-257748 provides a method of controlling the supply of fuel to a plurality of combustion chambers by a fuel controller comprising at least one fuel control trim valve, an orifice connected in series to the fuel control trim valve, and a fuel orifice connected in parallel to the fuel control trim valve.